High density information discs, such as video discs, carry much more information thereon than audio discs for example, and consequently pass a readout stylus at a much faster rate. For example, the usual audio discs revolve at about 33-78 rpm, whereas capacitance electronic discs, for example, revolve at about 450 rpm. If such a disc is placed on a smooth turntable, the disc will slip vis-a-vis the turntable during acceleration, which takes about five seconds to go from zero to 450 rpm and during deceleration, which takes about three seconds to go from 450 to zero rpm. Such slippage can damage the electronic disc and the readout stylus if the stylus sets down while the disc is not revolving at the expected rate.
Thus the turntable is being coated, at least at its periphery, with a comparatively thick, i.e., about 30/1,000" strip of cast PVC foam, or a foam rubber which can be natural or polyurethane rubber, for example. These strips are glued onto the edge of the turntable. This method is very expensive, both due to the material cost and to the high labor cost of applying the strip.
Several attempts have been made to spray-apply a friction coating to the turntable surface, which results in a much thinner coating and is much cheaper to apply. However, they have either been too tacky, which attracts dust or the like, or they have rapidly worn away after only a few plays of the disc.
Thus the search has continued for a friction coating which can be readily applied and which will withstand numerous plays.